This invention relates generally to hopper systems adapted for storing fluent material within a hopper and fluidizing the material for efficient unloading of the material from the hopper.
This invention is especially concerned with hopper systems of the type wherein a permeable membrane closely overlies the side wall of a hopper for fluidized unloading of fluent material contained within the hopper. In such systems, the hopper walls have ports for introducing pressurized air into the hopper with the air passing inwardly through the membrane to increase the flowability of finely ground materials (e.g., flour) within the hopper. Hopper systems which utilize permeable membranes typically require maintenance and are difficult to repair due to the manner in which the membrane is attached to the hopper. For example, the membrane is typically fastened directly to the hopper (or a frame inside the hopper) by means of bolts passing through holes in the membrane, and tearing of the membrane is quite common at these holes. Replacement of a torn membrane can be difficult since each bolt retaining the membrane to the hopper must be removed and replaced. Moreover, access to the membrane and retaining bolts in the hopper can be quite limited thereby compounding the difficulty involved in replacing a membrane. In addition to securement to the hopper (or a frame inside the hopper) by means of bolts, the membranes are sometimes stitched to the members of a framework closely overlying the side wall of the hopper to reduce the tendency of the membrane to billow inwardly away from the side wall of the hopper upon introduction of pressurized air through the hopper walls and membrane into the interior of the hopper. Removing a used membrane from such a framework and installing a new membrane thereto can be difficult due to the extensive amount of stitching involved in securing the membrane to the individual members of the framework.
Reference may be made to U.S. Pat. Nos. 2,924,487, 3,115,369, and 3,448,900 showing a variety of hopper systems utilizing a permeable membrane secured to the inside of a hopper. Reference may also be made to U.S. Pat. Nos. 3,173,725, 3,253,750, 4,081,110, and 4,383,766 which disclose hopper systems generally in the field of this invention.